Dynamometer



March 27, 1945. F. A. GARRETT DYNAMOMETER I Filed Feb. 1, 1944 5 Sheets-Sheet 1 12241427620) fizzrzczs ,4 Gar/e55 4 March 27, 1945. F. A. GARRETT 2,372,420

DYNAMOMETER Filed Feb. 1, 1944 Sheets-Sheet 2 March 27, 1945- F. A. GARRETT ,372,420

DYNAMOMETER Filed Feb. 1, 1944 5 Sheets-Sheet 3 I z z y.

March 27, 1945. F. A. GARRETT DYNAMOMETER Filed Feb. 1, 1944 TORGl-JE lN-LB5 LOAD 5 Sheets-Sheet 4 WM 329 mi? March 27, 1945. F. A. GARRETT DYNAMOMETER Filed Feb. 1, 1944 5 Sheets-Sheet 5 Patented Mar. 27, 1945 Application February 1, 1944, Serial No. 520,680 In Great Britain January 14, 1943 8 Claims. (Cl. 73 -134) This invention relates to absorption dynamometers and particularly those of the so-called Prony brake type employed for testing the brake horse power of electric motors and other power units.

Hitherto these have been only suitable for a particular rotation of the unit to be tested and although of simple and varied construction, many of them give unreliable and inaccurate readings.

In order to overcome the difiicult'y of fluctuating readings, one form is known in which a secondary lever is fulcrumed to the brake lever, the brake lever being rigidly connected to an upper brake shoe and the secondary lever being connected by a suspension bolt to a lower brake shoe which is also connected by another suspension bolt to the adjacent end of the brake lever.

The end of the secondary lever remote from the brake has a. knife edge or point for contact with a spring balance. A coiled compression spring is interposed :between the fulcrum and the ends of the two levers adjacent to the balance.

In use, when the \power unit is rotating, the friction set up between the brake and'the wheel on which it is applied causes a load to be applied to the spring balance from which the load given ofi by the power unit can be ascertained.

When the frictional load becomes unsteady,

thus tending momentarily to increase-the reading on the spring balance, the compression of the coiled spring is varied by an amount proportionate to such momentary increase, so that the load, through the secondary lever, is increased and the secondary lever moves about its fulcrum. The readings, therefore, are steady and the eifect of the compression spring between the two levers is to negative the momentary increase --referred to.

The invention consists in a dynamometer, of the above type, which is reversible, that is, it is suitable for use in testing a power unit irrespective of the direction of rotation of the brake drum or wheel to which it is applied, namely, whether the drum rotates in a clockwise or anticlockwise direction while the test is being performed, at the sametime assuring accurate and steady readings.

In the drawings:

Figure l is a somewhat diagrammatic side velevation of a simple form of dynamometer according to the invention.

Figure 2 is aside elevation of another form, some parts being broken away to show parts in section. v

7, Figures 3 and 4 are, respectively, a plan and an end elevation corresponding to Figure 2,.

Figurelf: is an elevation, half in section, of the boosters. J

Figure 6 is a sectional elevation of the lower part of one booster cylinder on a larger scale.

Figure 7 isa sectional elevation of the brake drum with the shoelinings shown engaging it, the section being taken on the line VII-VII, Figure 2.

, Figure 8 is a side elevation illustrating a modification of part of the form of dynamometer shown in Figures 2 to '7. I

Figure 9 is an end sectional, elevation on the line IX-IX, Figure 8. I I

In the form of dynamometer according to the invention illustrated by Figure l, a brake drum I is fixed on the shaft 2 which is or can be driven by the shaft of the power unit which is to be tested.

Two semi-circular brake shoes 3 and 4, are providedwith frictional linings 5 embracing the drum l.

The brake shoes 3 and 4 are pivotally connected together byapin 6 and are also pivotally connected respectively to brake levers l and 8 by pins 9 and I0. 1

. The brake show 3 has 2. lug H fitted with a screw l2 forming an adjustable abutment for engagement with a heel l3 on the adjacent end of the brake lever I, and the. brake. shoe 4 has a similarlug I4 and a screw 15 for engagement with a heel IE on the adjacent end of the brake lever 8. The brake levers I and 8 are pivotally connected together near the brake shoes by two link'rods I1 and fulcrum pins 18, there being a link rod I! on each side of the levers, only one being seen in Figure l.

The free ends is and 20 of the brake levers I. and 8 are shaped to accommodate a compression spring 2| which is provided with a cap 22 and an adjusting screw 23. The ends" l9 and 20 also have knife edges or points and 25 for engage-v ment, respectively; with spring balances 26 and At the beginning of a test, the screw 23 of the compression spring 2| is adjusted to cause the brake levers I and 8 t'o pivot about their fulcrum 'pins 18, [8 to applythe brake shoes 3 and 4 to the brake drum. The adjustable abutments, namely, the screws l2 and 15, are then set so that there is a space between each screw 12 and 1 5 and its respectiveheel l3 and l6.

When the shaft 2 of the power unit to be tested is rotating'in a'clockwisedirection, considered. with reference to Figure 1, the drum l tends to turn the brake shoes 3 and 4 in the 2 same direction. The space between the abutment screw l5 and the heel I 6 is reduced until the screw engages with the heel. At the same time,

the screw l2 recedes from the heel l3. Consequently, the lower brake lever 8 becomes the brake lever proper for the time being carrying the upper brake lever l upwards. to operate the spring balance or gauge 28. .The upper brake lever 1 isthen acting irrthe manner of a secondary lever b'eing fre'etojrhove about its fulcrum pin 48 should the frictional load become unsteady,

the spring 2| neutralizing or negativing the momentary increase, thus ensuring a steady reading on the spring balance. I

When the power unit to be tested rotates the drum l in an anticlockwise direction, theupper abutment screw l2 engages with the heel l3, and the lower abutment screw I5 recedes from the heel I5, the upper lever 1 becoming the brake lever proper and the lower brake lever becoming the secondary leverengaging with and operating the spring balance 21.

Thefo'rm ofdynamometer according to the invention illustrated by Figures 2 to 7 is similar to that above described with reference to Figure l, andcorresponding parts are indicated by similar reference numerals.

The compression spring between the brake levers is replaced; by a hydraulic device. This comprises twoplun'g'ers 28 pivoted together and con i nected to the upper brake lever 1 by a pin 29,1so that they are free to oscillate relativelyto the lever. Two cylinders 30, for the reception of the plungers 28, are similarly pivoted together and connected to the lower brake lever '8 by a pin 5 i 29', so that they are free to oscillaterela'tively to that lever. A cylinder and a plunger are arranged on each side of the brake levers, only one set being shown in Fig re 2.

These cylinders are conveniently termed loader cylinders. v} Twinfieiiib'le pipes 3| cohnect the cylinders 30 through a lsingle pipe 32 to a' distribution box '33 to which fluid; for instance oil, is delivered from a pump or so called booster 34. This coinprises'acylinderfl fitted with a plunger 36. The 15 .net e rare'ee into the cylinder by e hand operated screw} "A spring 3 8 is interposed betweeii a ca 39 un thescrew ,31 and heap 40 d' 5 -fi'h i b9? 33-. .ili iiel jil l 1 1. 112?! 3 i ir nr j te to mp oil so as to fill the distributing box 33, pipes}? an and remind rs -30, ,e rbeing a lowed to ess pe rom heie lie er h ou n h l a t ally; l ei yscrews 53 in theupper parts of hqllow, plungersja. Then, any desired pres- .sure can, beset up by forcing down the plunger by its screw, 31., If the pressure is to be reduced, the operating lever-His moved as indicated by the arrow 54, Figure'6 to lift the valve 5! off itsseat, and allow oil to escape back to thereseri oir 43.,.The pressureof the oil in the distributin box- 33am, therefore,- in the cylinders 30 is indicatedon a pressure gauge 55 which pe '52 connects the cylinis connected to the distributing box by a flexible pipe 56. I

By means of the booster 34, above described, the brake levers 1 and 8 can be moved about their fulcrum pins l8, l8, so as to apply the brake shoes 3 and 4 to the brake drum l, and the load so applied is indicated on the gauge 55. of this load being maintained during operation, the booster 35 is resilient owing to the spring 318 and consequently momentary increases in load can be neutralised or cancelled out, as is the case with the spring 2| above described with reference to the example shown in Figure 1.

A bracket 51, mounted on the base 58 of the 1 dynamometer, supports two hydraulic cylinders cylinders, so that the outward movements of the stems are thereby limited. These devices, com"- prising cylinders and plungers, are conveniently termed reactor cylinders.

The cylinders 59 and 60 are connected together by flexible pipes 6! and to a pressure gauge 69 by a pipe 68. They are supplied with oil under pressure, by a pipe 18, from a booster cylinder 10. This is of similar construction to'that of thebooster cylinder 34. Itcomprises a cylinder ll fitted with a plunger 12 which can be forced in by a screw 13 acting through a spring 14. arranged between caps 15 and 1.5. It has a ball valveat its. foot, similar to the ball valve 4| controlling'oi'l supplied from the reservoir 43 by a pipe 17. I Initially oilis pumped from the cylinder ll, through pipe 18 to the cylinder 60, and through pipe 51 to the cylinder 59. 'An'y air in the cylinders 59 and 99, during this initial filling, is allowed to escape through vents afterwards closed by screws :19 and 89. i

The brake drum 1 is hollow, as shown Figure 7. i

. When it is rotating, cooling water is fed into it by a pipe 8! and escapes under centrifugal action into an annular receiving trough 82 surrounding a central opening93 atone side. The water escapes between a conical discharge funnel 85 on the drum and a lip 85 on the trough.

'In 'orderto neutralise the weight of the brake shoes 3 and 4 and of the brake levers l and 8, they are "counterbalancedby Weights 36, 81 and 88. The weight 86 is attached to a cable 89 passing over pulleys 99 and 9| to the pin 6 of the brake shoes 3 and 4. Theweight 81 is attached to a cable 92 passing over pulleys '93 and 94 to the brake lever 1, and the weight 88 is attached to the cable 95 passing over pulleys 93 and 96 to the brake lever 8. The pulleys are supported between angle irons 9'! which are supported by the bracket 51 near one end, and by a bracket 98 near the other end. The bracket at is mounted onv bearing standards 99, 99 for the shaft 2 which I may be driven in any convenient manner by the shaft of the power unit to he tested, for eiz'a'niple by a driving belt on the grooved pulley H19.

In use, assuming that the shaft 2 and brake drum I are rotating In 'aclb'ck tvis direction; 05h- In spite sidered with reference to Figure 2, the screw I2 bears on theheel- I3 and there is a space between the screw and the heel I6. The brake levers 1 and 8 have tilted about their fulcrum pins. I8,-I8, sothat the knife edge or steel insert 25 of thelowerbrake lever 8 is in engagement with the point 66 of the stem 64 of the plunger 62 of the reactor cylinder 60, tending to push the plunger downwards but the travel is restricted by upward reaction of the hydraulic pressure. The knife edge or steel insert 24 of the upper brake lever 1 is disengaged from the point 65 of the plunger 6|. The upper brake lever 1 acts as the brake lever proper and the lower brake lever 8 becomes the secondary lever. The increased hydraulic pressure, due to .the pressure of the point 66, is indicated on the gauge 69.

-When the shaft 2 and the brake drum I are rotated in an anticlockwise direction, considered with reference to Figure 2, the upper brake lever 1 becomes the secondary lever and the lower brake lever B the brake lever proper as the screw I5 engages with the heel I6 andthere is clearance between the screw I2 and the heel I3. The knife edge or steel insert 24 engages with the point 85 of the stem 63 of the plunger 6| of the reaction cylinder 59 whichthen becomes operative, the resulting hydraulic pressure being indicated on the gauge 69.

- In a modification of the form of dynamometer just above described, the two reactor cylinders are replaced by a single reactor cylinder adapted to operate, by mechanical means,on the free ends of the brake levers. This modification is shown in Figures 8 and 9.

Only parts of the brake levers 1 and 8 are shown, it being assumed that the remainder are constructed and provided with loader cylinders 30 and brake mechanism as in the example shown in Figures 2 to 7.

A single reactor cylinder IN is arranged horizontally in alignment with ends I9 and and fixed between two rigidly mounted plates forming a frame I02. A flexible pipe 18 supplies oil underpressure to the cylinder-IN from a booster cylinder or pump, such as hereinbefore described with reference to Figure 5. A pipe I28 is connected toa pressure gauge 69.

The reactor plunger I03 has a stem or shank I04 of reduced diameter, theshoulder at the junction of the stem and plunger engaging with the adjacent end of the cylinder to form a stop. The

outer end portion I05 of the stem I04 is enlarged to carry a fulcrum pin I06 for a two-armed lever I01. The enlarged portion I05 can slide between guides I09 on the end of the cylinder IOI.

Bell-crank levers I09 and H0 are mounted respectively on fulcrum pins III and H2 carried by the lever I01. A cable H3 connected to the two levers I09 and H0 passes over pulleys H4, H5, mounted to rotate on pins H6, H1 carried by the frame I02. The cable II3 passes through holes H8, H9 in the ends I9 and 20 of the brake levers 1 and 8, and conical stops I20 and I2I are fixed on the cable adjacent to the holes. Their positions, relatively to the holes, are adjusted by adjusting trimmer screws I22 and I23 mounted in lugs on the lever I01.

The lever I01 has anti-friction rollers I24, I25 engaging with vertical fiat surface blocks I26 and I21 on the frame I02.

In operation, when the brake lever 1 rises and engages with the stop I20, it tends to move the cable H3 and thereby the lever I01, the roller I24 bearing hard against the block I26, and the 1 I claim:

roller I25 moving awayfrom the block I21. The lever I01 presses on the reactor plunger I03 and tends to move it into the cylinder IOI against the hydraulic pressure until a balance is effected, the pressure being indicated on the gauge 69.

When the brake lever 8 moves downwards into engagement with the stop I2I, the lever 101 is again moved by the cable, the roller I24 moving away from the block I26, and the roller I25 hearing hard on the block I21, the lever I01 again pressing on the reactor plunger I03 so that the pressure is again indicated on the gauge 69.

1. A reversible dynamometer comprising a brake drum, two brake shoes for application to the brake drum. said shoes being pivotally, connected together on one side of the centre of rotation of the drum, a brake lever pivotally connected to each of said shoes on the other side of said centre, an adjustable abutment on each shoe at a position between its two pivotal connections, for engagement with its respective brake lever, fulcrum pinsand links connecting the brake levers to gether and providing'fulcra for said levers near the brake shoes, adjustable and resilient means between the brake levers near the free ends thereof for applying load to the levers for loading the brake shoes, torque indicating means, and means for engagement, alternatively, with the free ends of the brake levers for operating said torque indicating means accordingly as the brake drum rotates in one direction or another.

2. A reversible dynamometer comprising a brake drum, two brake shoes for application to the brake drum, said shoes being pivotally connected together, a brake lever pivotally connected to eachbrake shoe, an adjustable abutment on each brake shoe for engagement with its respective brake lever, fulcrum pins and links connecting said brake levers together and providing fulcra for said levers near the brake shoes, adjustable and resilient means for applying load to the brake levers near their free ends for applying the brake shoes to the brake drum, hy-

draulic reacting cylinders having plungers for alternative engagement'withthe free ends of the brake levers accordingly as the brake drum rotates in one direction or another, means for sup- I plying liquid under pressure to said reacting cylinders, and a pressure gauge connected with said reacting cylinders for indicating the reacting force or torque load applied to the free end of the brake lever which is in engagement with a plunger.

3. A reversible. dynamometer comprising a brake drum, two brake shoes for application to the brake drum, said shoes being pivotally connected together, a-brake lever pivotally connected to each brake shoe, an adjustable abutment on each brake shoe for engagement with its respective brake lever, fulcrum pins and links connecting said brake levers together and providing fulcra for said levers near the brake shoes, loader hydraulic cylinders pivotally mounted on one brake lever near its free end, plungers for said cylinders pivotally mounted on the other brake lever, means for supplying liquid under pressure to said loader cylinders to apply load to the brake levers for applying the brake shoes'to the drum, and a pressure gauge for indicating the load applied by said loader cylinders, stationary hydraulic reactor cylinders having plungers for alternative engagement with the free ends of the brake levers accordingly as the brake drum rotates in one direction or another, means for supplying liquid underpressure'to said reactor cylinders, and a pressure gauge connected with said reactor cylinders for indicating the reacting force or torque load applied to the free end. of the brake lever which is in engagement with a plunger.

4. A reversible dynamometer as specified in claim 3 said means for supplying liquid under pressureto the reactor and loader cylinders, comprising in each case a pump cylinder and plunger, a screw for forcing the plunger into the cylinder to set up hydraulic pressure, and-a spring interposed between the screw and the plunger to provide a resilient connection therebetweenso that the reactor cylinders can react to neutralise momentary increases in load.

5. A reversible dynamometer as specified in claim 3 said means for supplying liquid under pressure to the loader cylinders, comprising a pump cylinder and a plunger, a'screw for forcing the plunger into the cylinder to set up hydraulic pressure, a spring interposed between the screw and the plunger, a reservoir for liquid, an automatic valve at the foot of the cylinder for controlling the flow of liquid from, the reservoir to the cylinder, and manually operable means for raising said valve from its seat Whenit is required to relieve the pressure of liquid in the cylinder.

6. A reversible dynamometer comprising a hollow brake drum, a shaft therefor having means for effecting a driving connection between it and a power unit to be tested, a central opening in oneside of said drum, a pipe for delivering cooling water into said drum, a gutter surrounding l ing fulcra for said levers near the brake shoes,

hydraulic loader cylinders pivotally mounted on one brake lever near its free end, plungers for said cylinders pivotally mounted on the other brake lever, means for supplying liquid under pressure to said loader cylinders to apply load to the brake levers for applying the brake shoes to the brake drum, '8. pressure gauge for indicating said-load, stationary hydraulic reactor cylinders having iplungers for'alternative engagement with the free ends of the brake levers accordingly as the brake drum rotates in one direction or another, means for supplying liquid under pressure to said-reactor cylinders, and a pressure gauge connected with said reactor cylinders for indicating the reacting force or torque load applied to the free end of the brake lever which is in engagement with a. plunger.

7. A reversible dynamometer comprising a brake drum, a shaft therefor, two brake shoes embracing said drum, said brake shoes being pivotally connected together, a brake lever pivotally connected to each brake shoe, an adjustable abutment on each shoe at a position between its two pivotal connections for engagement with its respective brake lever, fulcrum pins and links connecting the brake levers together and providing fulcra for said levers near the brake shoes, loader cylinders pivotally mounted on one of said brake levers near its free end, plungers for said cylinders pivotally mounted on the other brake lever, means for supplying liquid under pressure to said loader cylinders to apply load to the brake levers for applying the brake shoes to the brake drum, a pressure gauge for indicating. said load, a single stationary reactor cylinder arranged horizontally in alignment with the brake levers near the free ends thereof, a plunger for said reactor cylinder, a vertical two-armed lever pivotally mounted on the outer end of said plunger, a cable attached at its two ends to on- I posite ends of said lever, guide pulleys for guiding said cable vertically through holes in the free'ends of the brake levers, stops on said cable for alternatively engaging with said free ends adjacent to said holes according to thedirection of rotation of the brake drum, means for supplying liquid under pressure to said reactor cylinder and a pressure gauge connected therewith for indicating the reacting force or torque load on the end of thebrake a stop on the cable.

8. A reversible dynamometer asspecified in claim '7 having adjustable connections between the ends of the cable and the .ends of the twoarmed lever.

lever in engagement with FRANCIS ALBERT GARRETT. 

